#define _CRT_SECURE_NO_WARNINGS	

#include<stdio.h>
#include<math.h>

int main()
{
    int x1, y1, x2, y2;
    scanf("%d%d%d%d", &x1, &y1, &x2, &y2);
    printf("%.2f", sqrt((x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2)));
    return 0;
}